Wastewater holds great promise as a significant renewable energy resource; the energy laden in wastewater, if recovered, could provide up to 15-20% of the energy used in the U.S. The dilemma is that the primary fraction of this energy-potent material is sewage organic matter, which we use a significant amount of energy to remove, mainly by dissolving O2 gas into wastewater. Currently, wastewater treatment in the U.S. consumes ˜2% of energy; about 60% of this energy usage is dedicated to aeration of wastewater in the activated sludge process1. Algae-based wastewater treatment is gaining ground as an alternative to traditional treatment practices, because it has the potential to both, 1) treat wastewater without aeration, through the symbiotic growth of bacteria and photosynthetic microalgae (algae and cyanobacteria), and 2) preserve the chemical energy in wastewater in grown biomass. Thus, a successful microalgae process could substantially reduce energy usage for wastewater treatment and recover chemical energy from wastewater in the form of biofeedstock. However, engineering challenges limit the adoption of microalgae processes. For example, microalgae do not usually bioflocculate (naturally aggregate). The inability to bioflocculate results in ineffective separation of microalgae from water, and renders biomass recycling and harvesting, the two most important steps for bioprocess, difficult. This challenge, accompanied with the microalgae's need for light for photosynthesis, makes only certain reactor configurations, such as large open ponds, useful for microalgae processes, and they have been only limitedly used for treating wastewater in suburban and small community-based areas.
Formation of biogranules has been reported for some wastewater treatment and other bioengineered systems. One of the most well-studied biogranules is the aerobic granule sludge (AGS) that treats wastewater under aerobic conditions. It is considered that any kind of activated sludge could be developed to AGS when the growth selection pressure is met. Literature has shown that the selection pressure caused by unique process operations, such as short settling and effluent discharge times, induces the growth of activated sludge bacteria in granules, and this is the reason why AGS has been operated in a particular reactor configuration called sequencing batch reactor (SBR). The AGS process strictly depends on the artificial aeration for aerobic wastewater treatment and releases CO2 into the atmosphere; thus, challenges that are inherently associated with the conventional activated sludge process are still prevalent.
There is a need for improved biologically active compositions of matter that can assist in wastewater treatment and recovery of energy from wastewater.